1. Field of the Invention
The present invention relates to a page printer for printing data, received from a host unit, in units of pages of printing paper.
2. Description of the Related Art
Various types of page printers, such as LCD printers, LED printers, and laser printers, include a paper feed cassette for storing paper sheets used for print processing, and a paper discharge section for storing paper sheets for which print processing is completed. A paper sheet in the paper feed cassette is conveyed to an image forming section by a paper feed mechanism. A toner image formed by the image forming section is transferred onto the paper sheet. After the toner image on the paper sheet is fixed, the paper sheet is discharged to the paper discharge section.
In a printer of this type, in addition to a standard paper feed cassette arranged in the printer, a paper feed section for another type of paper feed cassette may be arranged to perform print processing with respect to paper sheets having different sizes or qualities. In a conventional printer, when paper feed is to be performed by using a plurality of paper feed cassettes in this manner, after an image is formed on a paper sheet fed from one paper feed cassette, and the paper sheet is completely discharged to the paper discharge section, another paper feed cassette is selected/designated to feed the next paper sheet from the other paper feed cassette. That is, when a paper feed cassette in use is to be switched to another cassette during a series of printing operations, paper feed from another paper feed cassette is started after a paper sheet which is conveyed in a convey mechanism is discharged to the paper discharge section.
In a page printer, as described above, a paper type in use is changed to another type in the following manner. After print processing for a paper sheet of a previous type is completed, and the paper sheet is discharged to the paper discharge section, a switching operation of the paper feed sections is performed. A paper sheet is fed from the paper feed section switched from the previous one, and printing processing is subsequently performed. Such a procedure is based on the scheme of a copying machine having a similar paper feed mechanism. In a copying machine, a change in paper size generally means a change in document size, and replacement of documents takes a little time. That is, there is no necessity to switch the paper feed sections instantly. Therefore, such a scheme poses no problems in the copying machines.
In a page printer, however, printing data transferred from a host unit corresponds to documents in a copying machine. If generation of image data to be printed out is performed at a high speed, paper feed is required almost incessantly regardless of image size. This necessity is increased with an increase in distance from a paper feed section to a standby portion of a paper sheet. Therefore, a switching operation of paper feed sections must be quickly performed in accordance with a change in size of a paper sheet for which printing is performed.
In the conventional printer having the above-described arrangement, however, the following problem is posed because its paper feed operation is based on the scheme of the conventional copying machines. In the conventional printer, even if it is analyzed that printing control data, received from a host unit during a printing operation, includes a paper feed cassette switching command, switching of paper feed cassettes cannot be performed unless a paper sheet which is conveyed in the convey mechanism is completely discharged into the paper discharge section. For this reason, when consecutive printing processing is to be performed while for example, paper sizes or paper qualities are sequentially changed, the paper printing rate per unit time (i.e., throughput) is decreased. Therefore, the conventional printer cannot efficiently perform print processing.